Recently, from a viewpoint of environment issues such as mercury-less, and for realizing a long-lived device, semiconductor light sources such as LED (light emitting diode) and laser are actively used as light sources for color image display devices. Major advantages of using semiconductor light sources include that displays with wide color reproduction ranges may be realized. This is because semiconductor light sources have sharp spectrums, and color image display devices using semiconductor light sources for three primary colors of red, green, and blue may have wider color reproduction ranges as compared to conventional color image display devices such as CRT (cathode ray tube) displays and liquid crystal displays using cold cathode fluorescent lamps. However, since saturation is increased in overall display due to the wider color reproduction ranges, colors are unnaturally reproduced such as a light blue sky is turned to be a deep blue sky or human skin to be yellow.
Since hues of red, green, and blue of semiconductor light sources are different from hues of the primary colors intended in input video signals, if the signals are directly displayed by color image display devices using semiconductor light sources for their light sources, reproduced videos have unnatural hues. For example, colors are unnaturally reproduced such as grass is displayed in bluish green since the green of semiconductor light source is bluish green having a shorter wave length and human skin is turned to be reddish since the red of semiconductor light source is crimson red having a longer wave length. To solve differences in hues in semiconductor light sources, for example, a color management technology of Patent Document 1 has been proposed.
In the invention described in Patent Document 1, in a color image display device having three primary colors with hues different from desired hues, an RGB video signal [R, G, B] is decomposed into three matrixes of respective primary-color components as follows.
                              (                                                    R                                                                    G                                                                    B                                              )                =                              (                                                            R                                                                              0                                                                              0                                                      )                    +                      (                                                            0                                                                              G                                                                              0                                                      )                    +                      (                                                            0                                                                              0                                                                              B                                                      )                                              [                  Expression          ⁢                                          ⁢          1                ]            
The decomposed components are converted with the use of constants a to i as follows.
                                          (                                                            R                                                                              0                                                                              0                                                      )                    ⇒                      (                                                                                a                    ×                    R                                                                                                                    d                    ×                    R                                                                                                                    g                    ×                    R                                                                        )                          ⁢                                  ⁢                              (                                                            0                                                                              G                                                                              0                                                      )                    ⇒                      (                                                                                b                    ×                    G                                                                                                                    e                    ×                    G                                                                                                                    h                    ×                    G                                                                        )                          ⁢                                  ⁢                              (                                                            0                                                                              0                                                                              B                                                      )                    ⇒                      (                                                                                c                    ×                    B                                                                                                                    f                    ×                    B                                                                                                                    i                    ×                    B                                                                        )                                              [                  Expression          ⁢                                          ⁢          2                ]            
The respective matrixes are summed to synthesize a converted RGB video signal [R′, G′, B′]
                                                                                                   (                                                                                                              R                          ′                                                                                                                                                              G                          ′                                                                                                                                                              B                          ′                                                                                                      )                                =                                ⁢                                                      (                                                                                                                        a                            ×                            R                                                                                                                                                                            d                            ×                            R                                                                                                                                                                            g                            ×                            R                                                                                                                )                                    +                                      (                                                                                                                        b                            ×                            G                                                                                                                                                                            e                            ×                            G                                                                                                                                                                            h                            ×                            G                                                                                                                )                                    +                                      (                                                                                                                        c                            ×                            B                                                                                                                                                                            f                            ×                            B                                                                                                                                                                            i                            ×                            B                                                                                                                )                                                                                                                          =                                ⁢                                  (                                                                                                                                          a                            ×                            R                                                    +                                                      b                            ×                            G                                                    +                                                      c                            ×                            B                                                                                                                                                                                                                    d                            ×                            R                                                    +                                                      e                            ×                            G                                                    +                                                      f                            ×                            B                                                                                                                                                                                                                    g                            ×                            R                                                    +                                                      h                            ×                            G                                                    +                                                      i                            ×                            B                                                                                                                                )                                                                                                        =                                ⁢                                                      (                                                                                            a                                                                          b                                                                          c                                                                                                                      d                                                                          e                                                                          f                                                                                                                      g                                                                          h                                                                          i                                                                                      )                                    ⁢                                      (                                                                                            R                                                                                                                      G                                                                                                                      B                                                                                      )                                                                                                          [                  Expression          ⁢                                          ⁢          3                ]            
This means that when red is displayed, a hue of the red to be displayed is changed by emitting light for not only red but also green and blue at a certain rate to acquire a desired hue.
FIG. 14 is a chromaticity diagram of conversion of color space using a conventional color conversion device. This is the u′v′ chromaticity diagram (CIE1976UCS chromaticity diagram) and, in this example, a method described in above Patent Document 1 is used to correct a hue in accordance with the sRGB standard color space established in IEC61933-2-1. It is well known that colors of two points on the half line drawn from a white chromaticity coordinate 000 toward a chromaticity coordinate of arbitrary color have the same hues and distances from the white chromaticity coordinate 000 generally correspond to saturations of the points.
Since chromaticity coordinates of the three primary colors of a color reproduction range 010 of the color image display device are not located on the half lines linking the white chromaticity coordinate 000 and the chromaticity coordinates of the three primary colors of the sRGB standard color space (color reproduction range of a video signal) 020, the hues are different from those of the primary colors of the sRGB standard color space 020. The video signal may be converted using the method disclosed in Patent Document 1 and reproduced as a color reproduction range 030. Since the chromaticity coordinates of the three primary colors of the color reproduction range 030 are shifted onto the half lines linking the white chromaticity coordinate 000 and the chromaticity coordinates of the three primary colors of the sRGB standard color space 020, the converted hues of the three primary colors become identical to the hues of the primary colors of the sRGB standard color space 020.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2000-278705